Electrical mercury cut-out



Nov. 13, 1934. H, woRsDALl. i 1,980,243

ELECTRICAL MERCURY CUT-OUT Filed Oct. 2l, 1951 2 Sheets-Sheet l NOV. 13, 1934.A H. WORSDALL 1,980,243

ELECTRI CAL MERCURY CUT OUT Filed Oct. 2l, 1931 2 Sheets-Sheet 2 Patented Nov. 13, 1934 UNITED STATES PATENT OFFICE ELECTRICAL MERCURY CUT-OUT Application October 21, 1931, Serial No. 570,205 In Great Britain December 23, 1930 14 Claims. (Cl. 200-113) This invention relates to electrical cut-outs of I the kind in which there is employed a column o1 mercury which normally forms an electrical connection between two contacts and is contained in a tube of insulating refractory material having a restricted bore in a portion thereof, in which the mercury parts when there is a predetermined overload of current.

According to this invention a mercury cut-out 0 comprises a refractory body having a comparatively narrow or restricted bore in said body, s'aid bore being adapted to receive a thread or column of mercury normally forming an electrical connection between two contacts, a reservoir of mercury beneath said bore, and a plunger mechanism associated with said reservoir whereby upon operation of said plunger mercury may be driven up from said reservoir into said bore to recomplete the electrical circuit.

It will be seen that the construction of mercury cut-out in accordance with this invention avoids the use of rubber bags and similar devices which have hitherto commonly been employed in mercury cut-outs and provides a cut-out which is electrically sound, simple and durable.

In constructions of cut-out in accordance with this invention and suitable for use for larger sizes the narrow or restricted bore in the refractory material preferably forms part of a closed path for the mercury the plunger mechanism being associated with said closed path so that when an overload occurs and a break is caused in the thread or column of mercury in the restricted or narrow bore this thread or column may be recompleted by operation of the plunger the said operation causing mercury to flow round the closed path.

Preferably the cut-out is enclosed in a casing of non-conducting material through which the contacts making connection to either end of the operating thread or column of mercury project.

The invention is illustrated in the accompanying drawings which show various arrangements in accordance therewith.

Figure 1 is a vertical sectional view of one embodiment of the invention, parts being shown in elevation;

Figure 2 is a view in rear elevation of the embodiment shown in Figure 1;

y Figure 3 is a horizontal sectional view taken on the line 3-3 of Figure 1;

Figure 4 is a vertical sectional view of a modi-` fied form of cut-out embodying the invention, parts being shown in elevation; v

Vhaving a restricted portion 2.

Figure 5 is a View similar to Figure 4 showing a further modification;

Figure 6 is a vertical sectional View of a further modiiication, parts being shown in elevation;

Figure '7 is a view in vertical section of a modi- 60 ed form of pressure creating mechanism;

Figure 8 is a View similar to Figure 7 showing an additional modified form of pressure creating mechanism;

Figure 9 is a vertical sectional view of a fur- 65 ther modication of pressure creating mechamsm;

Figure l0-is a vertical sectional view of a still further modification of pressure creating mechamsm;

. Figure 11 is a vertical sectional View of an assembled cut-out constructed in accordance with the invention with parts shown in elevation;

Figure 12 is a fragmentary view in iront elevation of an assembly in which a plurality of cutouts is provided with common operating means;

Figure 13 is a top plan View o the construction shown in Figure l2;

Figure 14 is a View in front elevation of an assembly in which a plurality of individual cut-outs is mounted on a control panel;

Figure 15 is a transverse vertical sectional view of the construction shown in Figure 14.

Referring to Figures 1, 2 and3 of the drawings which show in sectional elevation, rearl elevation, and sectional plan on the line 3-3 of Figure 1, one form of construction the cut-out here shown comprises a refractory body 1, having two bore holes formed therewithin one of said bore holes This restricted portion is adapted to contain the thread of mercury which is broken when too high a current flows therethrough. 'I'he two bores in the refractory body are indicated by the reference numerals 3 andl 4, the bore 3 containing the re- 95 stricted portion 2. The bores 3 and 4 communicate at the bottom so that in effect a reservoir of mercury beneath the bores is obtained. The lower communication between the bores is indicated at 5. The refractory body 1 is tted into an 100 insulating tube 6 which screws at one end into a metal cap 7 and at the other into a second metal cap 8. As will be seen the metal cap 7 forms as it were the bottom of the mercury reservoir, and also forms in effect one wall of the communicating passage 5. The metal cap 8 is formed with two bore holes, as shown, these bore holes communieating via the passage 9. Into one of the bore holes in the metal cap 8 is tted a. plunger 10 which is mounted upon a rod 11 adapted to be 110 depressed by a push button 12, the rod passing through a bearing member 13 screwed into the metal cap 8, the plunger being mounted for free sliding movements for creating pressure in the conduit. The other bore hole is closed at the top by a screwed plug 14. The whole device is enclosed and protected by an insulating shroud or cover 15 which is formed with a pair of apertures on its top face to pass the push button 12 and the rod 11 and upper portion of the bearing member 13.- As will be seen a spring 16 surrounds the rod 11 and serves to bias the plunger 10 upwards. Contact to the bottom of the mercury thread or column is made by means of a plug or similar connection device 17 passing through the shroud as shown and held against the cap 7 by a screw 18 screwing into the said cap. Connection to the other end of the mercury thread or column is made by means of a cable (not shown) in the circuit to be controlled, said cable being passed through a suitable aperture in the shroud into a recess or socket 19 formed in the cap 8 and its bared end clamped by the usual grub screw 20. It will be seen that with this arrangement if the overload operates the mercury column may be re-completed merely by depressing the push button 12 which will move the plunger 10 downwardly to create pressure in the conduit`4, the pressure acting on mercury in the reservoir to force mercury up into the restricted bore 2. Figure 4'shows an arrangement generally similar to that illustrated in Figure 1 the principal dierence being that in Figure 4 the bore 3 is not provided with a restricted portion but is made of the required diameter substantially throughout the whole of its length while a oat or non-return valve 21 is situated above the end of thebore in the refractory body 1. A further difference is that the plunger 10 operates not directly in ahbore hole formed in the cap 8 but in an insulating lining 22 positioned in said bore. 23 is an air vent which may be provided if desired not only in the construction shown in Figure 4 but in any other construction. In Figure 4 the air vent 23 appears to be stopped at its outer end by the insulating shroud 15 but in practice'the flt of the shroud about the assembled body of the cut-out is not suiiciently close to result in air-tightness. Figure 5 shows a further modified construction generally resembling Figure 4 but differing therefrom principally in .that the upper connecting passage 9 is omitted. In this arrangement the mercuryv col` umn is re-completed after the cut-out has trpped as in the previously described arrangement and in practice it is found that satisfactory operation can be obtained without providing a. closed or loop path for the mercury.

. In all the constructions of mercurycut-out illustrated a certain amount of back pressure reacting upon the plunger 10 will be generated when the mercury column is broken by an overload. This back pressure may be employed to give an indication that the overload has operated by so arranging the parts so that the back pressure can "kick-back the plunger 10 and push button 12 to a position higher than that occupied before operation, the plunger being held in this kick-back or higher position by friction. The form of construction illustrated in Figure 5 in which a closed or loop circuit for the mercury is not provided, is not so suitable for the larger sizes of mercury cut-out as are constructions, such as those illustrated in Figures 1 to 4.

Figure 6 shows in sectional elevation a simple form of construction suitable for use in Small sizes of mercury cut-out. In this construction the assembly consisting of the refractory body 1, tube 6, valve 21, plug 14, and end cap 8a (which is screwed on to one end of the tube 6) is screwed by means of a thread formed on the other end of the tube 6 into a base-piece 7a into which also screws a plunger assembly as shown. This form of construction oiers the advantage that the plunger assembly may be arranged quite conveniently at a considerable distance from that part of the apparatus in which the column or thread of mercury is situated. Where the circuit to be controlled is at a high voltage this arrangement presents obvious advantages of safety and in such cases the cylinder in which the plunger operates should be made of glass or other suitable insulating material.

In several of the structures in accordance with this invention and more particularly in structures s'uch as those illustrated in Figures 5 and 6 where there is no loop circuit for the mercury, it is desirable to provide means for preventing the mercury column or thread from being broken after having been re-completed when the button is released after the re-setting operation. Referring, for example, to Figure 4 it will be seen that just as the push button is pressed the mercury is forced into the bore in the refractory body, so, when the button is released, there is a tendency for the mercury to be sucked out of said bore. This difliculty may be met in numerous ways. For example, in the arrangement shown in Figure 6 the cylinder 24 in which the plunger 10 moves is enlarged over a portion of its length as shown, the narrow portion (which ts closely about the said plunger) being of lesser length than the stroke. When in this construction the push button 12 is depressed pressure will be transmitted to the mercury through a certain amount of air which will be present (which air will, of course, be compressed on depression of the push button 12) and the mercury will accordingly be forced into the narrow bore. When, however, the push button 12 is fully depressed the plunger 10 travels beyond the close fitting portion of the cylinder in which it works and accordingly permits the trapped compressed air to escape past the said plunger and out through the air hole 23. Other arrangements of plunger mechanisms for serving the same purpose are shown in Figures 7, 8 and 9. In Figure '1 the push button 12 is formed in two parts 12a. 12b which are spring biased by means of springs 12e away from one another, the separation being limited by set screws 12d as shown. A bore hole 11a isformed through the rod 11 this bore hole communicating with a similar bore hole 10a in the plunger. It will be seen that with this arrangement when the push button 12 is depressed the air escape passage which is via the bore holes 10a 11a and then out between the parts 12a and 12b will be closed, but when the downward pressure of the finger ceases the air escape passage is opened. In the modied form shown in Figure 8 a similar eiect is obtained, but in this case the push button is of simple construction, and is merely provided with a small hole or bore 12e communicating as Abefore with bore holes 11a and 10a. When the finger is placed over the push button 12 to depress it, the upper that when the push button 1'2 is depressed so that the plunger is moved past the peripheral groove compressed air can escape from one side of the plunger to the other via the said groove. The

peripheral groove 25 also permits the transfer of mercury from the upper to the lower side of the plunger during the upward stroke of said plunger in the case in which the .plunger mechanism is employed in a cut-out having a loop or closed path for the mercury (the case envisaged in Figure 9).

In certain cases, more especially in very small sizes, it is not necessary to provide means for overcoming this suction eiect it being suicient to provide a simple plunger with limited travel. A simple arrangement of plunger mechanism without special means of air escape is illustrated in Figure 10.

Figure 1l shows in schematic sectional elevation an assembled cut-out in accordance with the present invention arranged in a suitable box or container and adapted to be operated by a tumbler switch handle 26. This construction is very suitable for use in connection with double pole arrangements in which case two mercury cut-outs side by side may be arranged within the box and their operating push buttons connected together by a transverse link which is operated by the tumbler switch. A somewhat similar multiple mercury cut-out assembly in which the cut-outs are operated in common is shown in Figures 12 and 13 which figures show an arrangement of three phase circuit breaker there being provided three mercury cut-outs with their operating push lgltons linked together and to a master button Mercury cut-outs in accordance with this invention are exceedingly small and compact, for example, Figures l2 and 13 show full size a three phase circuit breaker suitable for use for sizes up to about 20 amperes. This small size makes the cut-outs very convenient for arrangement in banks for control of a plurality of circuits. A control panel incorporating a number of mercury cut-outs is shown in Figures 14 and 15, 27 being a glass front. If, as is preferable, the mercurcy cut-outs employed in a control panel of this kind are so constructed that theA push button operating knobs will be forced upwards by back pressure when over-load occurs, it will be possible to see at a glance the failure of any circuits.

Although the particular forms of mercury cutout hereinbefore described are of the type in which the mercury thread or column which is adapted to be broken upon overload is heated directly by the passage of current therethrough obviously the invention is not limited to cut-outs of this type. This type is preferred because of its greater simplicity but, if desired, (for example in the case of very large sizes or in cases where a delay or lag in operation is required) the mercury thread or column may be heated indirectly as by a heating coil arranged in any convenient way and adapted to receive the operating current. Such a heating coil is indicated at HC in Figure 6. It will be obvious to those skilled in the art that indirect heating may be resorted to in any construction in accordance with this invention in a similar manner, and that other arrangements in a heating coil are possible.

It will'be noted that it is possible to employ a cut-out in accordance with this invention as a switch by suitably operating the plunger push button so as to obtain a suction eiect suicient to break the mercury thread or column although in all cases the thread or column will not be broken if the plunger push button is merely depressed and released as is the usual operation for re-setting.

It will further be noted that the U-tube like construction employed in the illustrated embodiments of this invention enables the convenient utilization of relatively long cores and the adoption of designs in which the voltage distribution in the cut-out is such as to render it safe and suitable for high tension working. Further, when the mercury column or thread breaks on overload the gases generated can not only escape upwards but also expand downwards and into the plunger cylinder.

What I claim is:-

l. A mercury eut-out comprising a body of insulation having a rst bore provided with a relatively narrow portion or constriction intermediate its ends, electrical contact members in electrical connection with the interior of said bore at points above and below the narrow or constricted portion thereof, a mercury reservoir beneath said bore, a conduit additional to said bore for transmitting pressure to said reservoir for driving mercury from said reservoir into said bore to electrically connect said contact members, and a plunger mechanism comprising a plunger mounted for free sliding movements in said conduit for creating pressure therein, said conduit, reservoir, and bore together forming a U-tube of which the said reservoir forms the bottom limb of the U, said conduit forming one of the remaining limbs and said bore the other limb, said plunger being free to be driven upwards in said conduit when pressure is generated as a result of rupture of the mercury column which normally makes connection between said electrical contact members.

2. In a mercury cut-out as set forth in claim l, having a path for mercury interconnecting the upper ends of the limbs of said U tube, whereby there is formed a closed loop path for mercury.

3. A mercury cut-out as set forth in claim l and wherein the conduit consists of a second bore in the said body, said body having a path for mercury interconnecting the upper ends of the two bores therein whereby there is formed a closed loop path for mercury.

4. A mercury cut-out comprising a body of insulating material having therein a rst bore provided with a relativelyV narrow portion or constriction intermediate its ends, a non-return valve located at the upper end of said bore and forming when seated a closure for said bore, electrical contact members in electrical connection with the interior of said bore at points above and below the narrow or constricted portion thereof, a mercury reservoir beneath said bore, a conduit additional to said bore for transmitting pressure to said reservoir for driving mercury from said reservoir into said bore to electrically connect said contact members, and a plunger mechanism comprising a plunger mounted for free sliding movements in said conduit for creating pressure therein, vsaid conduit, reservoir, and bore together forming a U-tube of which the said reservoir forms the bottom limb of the U, said conduit forming one of the remaining limbs and said bore the other limb, said plunger being free to be driven upwards in said conduit when pressure is generated as a result of rupture of the mercury column which normally makes connection between said electrical contact members.

5. A mercury cut-out as set forth in claim including means for releasing air pressure accumulated during movement of said plunger in said cylinder to recomplete the mercury column in the bore.

6. A mercury cut-out as set forth in claim 1 including means having a passage leading from the outside air to the pressure face of the plunger, and means operable automatically upon depression of said plunger for closing said passage for releasing air pressure accumulated during movement of said plunger in said cylinder to recomplete the mercury column in the bore.

7. A mercury cut-out as set forth in claim 1 including means having a bypass leading from the pressure face to the rear face of the plunger, said bypass being positioned to function when said plunger is approaching its fully depressed position to release air pressure accumulated during movement of said plunger in said cylinder to recomplete the mercury column in the bore.

v8. A mercury cut-out comprising a body of refractory insulating material having a narrow bore therein, contact means for making electrical connection with the interior of said bore at opposite ends thereof, a mercury reservoir attached to the lower end of said body and communicating with the bore therein, a conduit communicating with said reservoir for transmitting pressure to said reservoir for driving mercury from said reservoir into said bore, said conduit, mercury reservoir, and bore together constituting a U-tube structure of which the said reservoir forms the bottom limb of the U, said conduit forming one of the remaining limbs and said bore forming the third limb, a plunger mechanism comprising a plunger mounted for free sliding movements in said conduit for creating pressure therein, said plunger being free to be driven upwards in said conduit when pressure is generated as a result of rupture of the mercury column in said bore.

9. A mercury cut-out comprising means including a body of insulation having a bore provided with a relatively narrow portion or constriction intermediate its ends, electrical contact members in electrical connection with the interior of said bore at pointsl above and below the narrow or constricted portion thereof, a mer'cury reservoir beneath said bore, a conduit additional to said bore for transmitting pressure to said reservoir for driving mercury from said reservoir into said bore to electrically connect said contact members, and a plunger mechanism comprising a plunger mounted for free sliding movements in said conduit for creating pressure therein, said conduit, reservoir, and bore together forming a U-tube of which the said reservoir forms the bottom limb of the U, said conduit forming one of the remaining limbs and said bore the other limb, said plunger `being free to be driven upwards in said conduit when pressure is generated as a result of rupture of the mercury column which normally makes connection between said electrical contact members.

10. A mercury cut-out as set forth in claim 8 and including a non-return valve at the upper end of the bore containing the mercury column, said valve when sealed forming a closure for said bore.

11. A mercury cut-out as set forth in claim 4 and having a path for mercury interconnecting the upper ends of the limbs of said U-tube whereby there is formed a closed loop path for mercury.

12. A mercury cut-out as set forth in claim 4 including means for releasing air pressure accumulated during movement of said plunger in said cylinder to recomplete the mercury column in the bore.

13. An electrical cut-out of the class described, including an insulating tube of narrow bore, a mercury column filling said bore, a metallic piece at each end of the tube in electrical contact with the corresponding end of the mercury column, a metallic contact member engaged with each metallic piece and serving to connect the mercury column in an electrical circuit to Abe controlled by the cut-out, a chamber in free communication with one endof the bore of the tube and into which mercury is expelled from the tube when the mercury column is ruptured due to the'current in the electrical circuit exceeding a predetermined maximum value, means, independent of the action of gravity and operative while the cut-out is maintained in its normal position, for positively forcing mercury discharged into said chamber by rupture back into the tube and means for positively preventing return of mercury to the tube until said forcing means is operated.

14. An electrical cut-out of the class described lll'll comprising an insulating tube of narrow bore,

a mercury column lling said bore, a metallic piece at each end of the tube in electrical contact with the corresponding end of the mercury column, a

metallic contact member engaged with each me- 1 tallic piece and serving to connect the mercury column into an electrical circuit to be controlled by the cut-out, a chamber in free communication with one end of the bore of the tube and into which mercury is Aexpelled from the tube when the mercury column is ruptured due to the current in the electrical circuit exceeding a predetermined maximum value, an extension of said chamber arranged laterally of said insulating tube and communicating with that end of said tube remote from the main expansion chamber, means independent of the action of gravity and operative while the cut-out is maintained in its normal position, located in said extension for positively forcing mercury back into the tube and means for preventing return of mercury to the tube until said forcing means is operated.

HORACE WORSDALL. 

